Organic
bulk heterojunction (BHJ) solar cells are a promising alternative
for future clean-energy applications. However, to become attractive
for consumer applications, such as wearable, flexible, or semitransparent
power-generating electronics, they need to be manufactured by high-throughput,
low-cost, large-area-capable printing techniques. However, most research
reported on BHJ solar cells is conducted using spin coating, a single
batch fabrication method, thus limiting the reported results to the
research lab. In this work, we investigate the morphology of solution-sheared
films for BHJ solar cell applications, using the widely studied model
blend P3HT:PCBM. Solution shearing is a coating technique that is
upscalable to industrial manufacturing processes and has demonstrated
to yield record performance organic field-effect transistors. Using
grazing incident small-angle X-ray scattering, grazing incident wide-angle
X-ray scattering, and UV–vis spectroscopy, we investigate the
influence of solvent, film drying time, and substrate temperature
on P3HT aggregation, conjugation length, crystallite orientation,
and PCBM domain size. One important finding of this study is that,
in contrast to spin-coated films, the P3HT molecular orientation can
be controlled by the substrate chemistry, with PEDOT:PSS substrates
yielding face-on orientation at the substrate–film interface,
an orientation highly favorable for organic solar cells.
The supramolecular structure essentially determines the properties of organic thin films. Therefore, it is of utmost importance to understand the influence of molecular structure modifications on supramolecular structure formation. In this article, we demonstrate how to tune molecular orientations of amphiphilic 4-hydroxy thiazole derivatives by means of the Langmuir-Blodgett (LB) technique and how this depends on the length of an alkylic spacer between the thiazole chromophore and the polar anchor group. Therefore, we characterize their corresponding supramolecular structures, thermodynamic, absorption, and fluorescence properties. Particularly, the polarization-dependence of the fluorescence is analyzed to deduce molecular orientations and their possible changes after annealing, i.e., to characterize the thermodynamic stability of the individual solid state phases. Because the investigated thiazoles are amphiphilic, the different solid state phases can be formed and be controlled by means of the Langmuir-Blodgett (LB) technique. This technique also allows to deduce atomistic supramolecular structure motives of the individual solid phases and to characterize their thermodynamic stabilities. Utilizing the LB technique, we demonstrate that subtle molecular changes, like the variation in spacer length, can yield entirely different solid state phases with distinct supramolecular structures and properties.
Processing of 4-alkoxythiazole sulfonamidesviathe Langmuir–Blodgett technique gave an insight into the influence of aggregation on the electro-optical properties of thin films.
A series of new dihydrotetraazaanthracenes and one new dihydrotetraazatetracene as substances for applications in organoelectronic devices and as suitable building blocks for higher azaacenes was synthesised. The condensation of aromatic diamines with dichlorodicyanopyrazine led to these tricyclic/tetracyclic compounds. Syntheses of N-substituted phenylenediamines were developed to enable the introduction of multiple functional groups such as ester, amino, or nitro groups on the chromophoric system. Relationships between the structure and the spectroscopic properties could be derived from UV/Vis absorption and fluorescence spectroscopy, as well as by DFT and TD-DFT calculations of molecular and aggregate structures. The absorption spectra are dominated by π-π* transitions of the single molecules, whereas aggregation needs to be taken into account to obtain reasonable agreement between theory and experiment in certain cases. Single-crystal X-ray analyses were carried out to examine the morphology and solid packing effects. Finally, a dihydrotetraazaanthracene was used as a building-block to create a mesoionic octaazapentacene.
Effective core potential integral and gradient evaluations are accelerated via implementation on graphical processing units (GPUs). Two simple formulas are proposed to estimate the upper bounds of the integrals, and these are used for screening. A sorting strategy is designed to balance the workload between GPU threads properly. Significant improvements in performance and reduced scaling with system size are observed when combining the screening and sorting methods, and the calculations are highly efficient for systems containing up to 10 000 basis functions. The GPU implementation preserves the precision of the calculation; the ground state Hartree-Fock energy achieves good accuracy for CdSe and ZnTe nanocrystals, and energy is well conserved in ab initio molecular dynamics simulations.
Manganese dimers on Ag(111) are investigated with scanning tunneling microscopy and density functional calculations. Two species of dimers coexist that differ in their apparent heights and the absence or presence of submolecular structure. These species can be interconverted by electron and hole injection from the microscope tip. Calculations identify the two kinds of dimers as pristine Mn 2 and Mn H 2 and show that hydrogen attachment to Mn 2 leads to marked changes in the dimer electronic and magnetic structure. Antiferromagnetic coupling between Mn magnetic moments in Mn H 2 leaves its spectroscopic signature in the electronic structure of the monohydride compound.
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